Infant survivors of Idiopathic Respiratory Distress Syndrome (RDS) develop pulmonary residua which are believed to predispose these infants to more frequent and severe respiratory infections. To assess this aspect of the long-term morbidity of RDS, it is proposed to systematically and prospectively evaluate the frequency, severity, and etiologies of subsequent acute respiratory illnesses in survivors of RDS, preterm infants who did not have RDS, and normal infants. If RDS survivors are at increased risk of more frequent or more severe respiratory illnesses, it is essential to determine whether the infections are more severe manifestations of the "usual" respiratory pathogens of this age group or due to an increased susceptibility to organisms which uncommonly cause disease in normal infants.